$1 \ L$ each of gases $A$ and $B$ diffused through a membrane in $15$ and $30$ minutes,respectively,under identical conditions. What is the ratio of molecular weight of $A$ and $B$?

In which of the following gas mixtures does Dalton's Law of Partial Pressure not apply? Why?
$(i)$ $CO_2 + O_2 + N_2$
$(ii)$ $CO + O_2$
$(iii)$ $NH_3 + HCl$
$(iv)$ $HCl + O_2$

At $27^{\circ} C$,a closed vessel contains a mixture of equal weights of helium (mol. wt. = $4$),methane (mol. wt. = $16$) and sulphur dioxide (mol. wt. = $64$). The pressure exerted by the mixture is $210 \ mm$. If the partial pressures of helium,methane and sulphur dioxide are $p_1, p_2$ and $p_3$ respectively,which one of the following is correct?

When an equal weight mixture of $SO_2$ and $O_2$ is taken in an empty container,the ratio of the partial pressure of $O_2$ to the total pressure is ......

The total pressure of a mixture of two gases is equal to .......

Which has higher density: dry air or moist air? Why?